This invention concerns a method and apparatus for conditioning an electronic component having a characteristic subject to distortion following a change in temperature.
Highly accurate electronic measuring or generating instruments such as DMMs, calibrators and transfer standards utilise precision electronic components as their internal reference sources. Sometimes these components are used virtually in isolation as transfer standards. Most common of these components is the zener diode or composite zener/transistor reference used for voltage references and the resistor used as a resistance or impedance reference.
For highest accuracies these components are usually operated at a controlled temperature either to limit errors due to variation of reference value with temperature or to protect the component from permanent or semi-permanent change in value due to operation at a non-normal temperature. It is the latter situation which is of interest because, typically, components subjected to temperature excursions away from their normal operating temperature exhibit a memory effect where the reference value changes following the temperature excursion and may or may not recover over a period of time. This is commonly referred to as temperature hysteresis and is thought to be due largely to mechanical stress being induced by the temperature excursion and some of it being "locked in".
However, when components of an apparatus have been subjected to extremes of temperature such as may occur during transport, even the subsequent operation thereof at a controlled temperature may be insufficient to restore such induced changes, and the accuracy of the apparatus will therefore become affected by gradual changes in the characteristics of precision components, or by a permanent but not irreversible stepwise change in value.